ON THE PRECISION OF STEREOMETRIC SYSTEMS ) 
  
INTRODUCTION 
In structural engineering, experimental research on 
model structures is often used to determine material proper- 
ties and design criteria. While analytic solutions for 
problems in shells, plates, and space frames are available for 
different configurations and boundary conditions, these solu- 
tions are, by necessity, limited to simple cases and idealized 
boundary conditions. Numerical solutions, which have become 
increasingly practical and popular because of the recent inno- 
vations in computer science, are generally based on certain 
assumptions of boundary conditions and restraints. Experi- 
mental structural analysis, conducted on carefully made models, 
incorporates such conditions (Lenschow and Sozen, 1966). In 
structural analysis one of two approaches is used: direct or 
indirect. |n the direct approach, the necessary information 
is deduced from strain measurements. Strain gauges, however, 
fail to register in the plastic range of loading, and thus strain 
measurements have to be limited to the elastic range of loading. 
Fortunately, under relatively small loads, the tested material 
(steel, reinforced concrete, etc.) can be considered to have 
elastic properties (Wood, 1961). Elastic design criteria, 
however, are of restricted value, inasmuch as they are not 
valid for greater loads under which the plastic properties of 
the tested material become pronounced. Unfortunately, this is 
always the case near the yield point. 
  
1) The term ''Stereometric System is used to refer to a 
photogrammetric system in which one or more stereometric cameras 
are used for data acquisition.